1. Field of the Invention
The present invention relates to a piezoelectric resonator using bending vibration, and a piezoelectric component.
2. Description of the Related Art
Conventionally, band resonators having a frequency of 300 kHz to 800 kHz have used the radial vibration of a ceramic piezoelectric element. A piezoelectric resonator 1 (hereinafter, referred to as a radial resonator) utilizing the radial vibration is constructed by forming surface electrodes 3 on the front surface and back surface of a square piezoelectric substrate 2, and polarization-treating the piezoelectric substrate 2 in the direction perpendicular to the main surfaces of the piezoelectric substrate 2, as shown in FIG. 1 (the polarization direction of the piezoelectric substrate 2 is indicated by arrows in FIG. 1). Regarding the above-mentioned radial resonator 1, when a signal is applied across the surface electrodes 3, the piezoelectric substrate 2 is expanded and deformed in a direction toward the periphery of the substrate 2 in a plane that is parallel to both main surfaces.
Regarding the radial resonator 1, the product of the length of one side and the resonant frequency fr is substantially constant, and expressed by: Lsxc3x97fr=Cs, in which Cs represents a constant, that is, Cs≅2100 mmxc2x7kHz;. For example, if a resonator having the resonant frequency as fr=350 kHz is desired, the length Ls of one side of the resonator is 6 mm.
However, the size of such a component is not acceptable or usable in electronic components which require lighter, thinner, and shorter components. Thus, much smaller piezoelectric resonators are required.
To solve the above-described technical problems, preferred embodiments of the present invention provide a piezoelectric resonator utilizing bending vibration, having a very small and greatly reduced size, and a piezoelectric component including such a piezoelectric resonator.
According to the first preferred embodiment of the present invention, a piezoelectric resonator includes piezoelectric layers disposed on both surfaces of an internal electrode, respectively, and surface electrodes disposed on the outer main surfaces of the piezoelectric layer, respectively, both the piezoelectric layers being polarized so that the polarization directions of both the piezoelectric layers are substantially perpendicular to the inner electrode, and are opposite to each other with respect to the internal electrode.
Regarding the above-described piezoelectric resonator, when a signal is applied between both the surface electrodes, the resonator is deflected so as to become convex or concave, that is, so as to be bending-deformed on the main surfaces thereof. In this vibration mode, the constant that represents the product of the length of one side of the piezoelectric resonator and the resonant frequency decreases. Thus, the length of one side of the piezoelectric resonator can be shortened if the same frequency band is used. Thus, the size of the piezoelectric resonator can be greatly reduced.
Preferably, the piezoelectric resonator is placed in a case and supported at the nodes or the vicinities of the nodes of the piezoelectric resonator, and external terminals electrically connected to the surface electrodes of the piezoelectric resonator are provided on the outside of the case.
Since the piezoelectric resonator according to this preferred embodiment of the present invention is placed in the case, and the external terminals are provided on the outside of the case, the piezoelectric component can be downsized and the same frequency band is used. Further, since the piezoelectric resonator in the case is supported at the nodes or the vicinities of the nodes, damping of the vibration is prevented even though the piezoelectric resonator is mounted in the case.
Also preferably, in the piezoelectric component according to this preferred embodiment of the present invention, the case includes a case body and a cap covering the base body, protuberances provided on one of the upper surface of the case body and the lower surface of the cap are contacted with the nodes or the vicinities of the nodes of the piezoelectric resonator, and the nodes or the vicinities of the nodes of the piezoelectric resonator are elastically pressed by a metallic spring terminal inserted between the other of the upper surface of the base body and the lower surface of the cap, and the piezoelectric resonator. The term xe2x80x9celectro-conductive capxe2x80x9d includes a cap made of an insulation material, having an electro-conductive film disposed on the surface thereof, in addition to a cap made of a material having electro-conductive properties.
In this instance, since one of the lower surface or the upper surface of the piezoelectric resonator is pressed by protuberances, and the other is pressed by the metallic spring terminal, only one metallic spring terminal is required, and therefore, the cost is greatly reduced and assemblage of the piezoelectric component is easily performed.
Still preferably, the case includes a case body and an electro-conductive cap covering the case body, a pair of the external electrodes are provided on the lower surface of the case body, a pair of internal connection electrodes connected to the external electrodes, respectively, are provided on the upper surface of the case body, Liprotuberances provided on the upper surface of the case body are contacted with the nodes of the piezoelectric resonator and the vicinities of the nodes, at least one of the protuberances includes an electro-conductive material and is arranged on one of the internal connection electrodes, the nodes and the vicinities of the nodes of the piezoelectric resonator are elastically pressed by a metallic spring terminal inserted between the lower surface of the cap and the piezoelectric resonator, and the metallic spring terminal is electrically connected to the other internal connection electrode via the cap.
Accordingly, since the lower surface of the piezoelectric resonator is supported by the protuberances, and only the upper surface thereof is pressed by the metallic spring terminal, only one metallic spring terminal is required. Thus, the cost is greatly reduced and assemblage of the piezoelectric component is easily performed. Moreover, since at least one of the protuberances is preferably made of an electro-conductive material and arranged on one of the internal connection electrodes, the nodes or the vicinities of the nodes of the piezoelectric resonator are elastically pressed by the metallic spring terminal inserted between the lower surface of the cap and the piezoelectric resonator, and the metallic spring terminal is electrically connected to the other internal connection electrode via the cap, one of the surface electrodes of the piezoelectric resonator can be electrically connected to one of the external terminals via the electro-conductive protuberance, and the other surface electrode of the piezoelectric resonator can be electrically connected to the other external terminal via the metallic spring terminal and the electro-conductive cap. Thus, wiring connection steps for connecting lead wires can be omitted.
Preferably, the case includes a case body and a cap covering the case body, and a first metallic spring terminal, the piezoelectric resonator, and a second metallic spring terminal are inserted between the case body and the cap, and the nodes or the vicinities of the nodes of the piezoelectric resonator are elastically pressed by both the metallic spring terminals.
Since the piezoelectric resonator is sandwiched and held between the metallic spring terminals from both sides thereof, the piezoelectric resonator is very securely supported, due to the elasticity of both the metallic spring terminals.
Still preferably, the case includes a case body and an electro-conductive cap covering the case body. A pair of the external terminals are provided on the lower surface of the case body. A pair of the internal connection electrodes that are electrically connected to the respective external terminals are provided on the upper surface of the case body. A first metallic spring terminal, the piezoelectric resonator, and a second metallic spring terminal are inserted between the case body and the cap. The nodes and the vicinities of the nodes of the piezoelectric resonator are elastically sandwiched and held between both the metallic spring terminals. The first metallic spring terminal positioned on the lower surface of the piezoelectric resonator is in contact with one of the internal connection electrodes. The second metallic spring terminal positioned on the upper surface of the piezoelectric resonator is electrically connected to the other internal connection electrode via the cap.
Since the piezoelectric resonator is sandwiched and held by the metallic spring terminals from both sides thereof, the piezoelectric resonator is securely supported, due to the elasticity of both the metallic spring terminals. Further, since the first metallic spring terminal positioned on the lower surface of the piezoelectric resonator is in contact with one of the internal connection electrodes, and the second metallic spring terminal positioned on the upper surface of the piezoelectric resonator is electrically connected to the other internal connection electrode, one of the surface electrodes of the piezoelectric resonator can be electrically connected to one of the external terminals via the first metallic spring terminal, and the other surface electrode of the piezoelectric resonator can be electrically connected to the other external terminal via the second metallic spring terminal and the electro-conductive cap. Thus, wiring connection steps using lead wires or the like can be omitted.
Also preferably, the piezoelectric resonator is mounted and accurately located by positioning portions arranged to protrude from the inner peripheral surface of the case body, at the positions thereof opposed to the respective nodes and the vicinities of the nodes of the piezoelectric resonator, and the metallic spring terminal is positioned by inserting the end portions of the metallic spring terminal into concavities formed in at least a portion of the positioning portions.
As described above, since the metallic spring terminals are positioned by utilizing the positioning portions for positioning the piezoelectric resonator, the structure of the case body is greatly simplified. In addition, since the metallic spring terminal is positioned by inserting the end portions of the metallic spring terminal into the concavities of the positioning portions, the metallic spring terminal is securely positioned.
Still preferably, since the piezoelectric resonator is positioned by the positioning portions protruding from the inner peripheral surface of the case body, at the positions thereof opposed to the respective nodes and the vicinities of the nodes of the piezoelectric resonator, and the end surfaces of the metallic spring terminal are contacted with the positioning portions at least at two positions whereby the metallic spring terminal is prevented from rotating.
Since the metallic spring terminal is positioned by utilizing the positioning portions for positioning the piezoelectric resonator, the structure of the case body itself is greatly simplified. Further, since the positioning portions are contacted with the end surfaces of the metallic spring terminal, whereby the metallic spring terminal is prevented from rotating, the structure of the positioning portions is not complicated, and the incorporation of the metallic spring terminal is easily performed.
A load capacitance element may be mounted on the case body in the space between the metallic spring terminal arranged on the lower surface of the piezoelectric resonator and the case body.
Since the load capacitance element is mounted in the space between the metallic spring terminal and the case body, the load capacitance element can be mounted without the outer dimension of the piezoelectric component being Li increased.
Also preferably, the case includes an inner case and an outer case having a box shape to accommodate the inner case, the piezoelectric resonator inclined by about 45xc2x0 relative to the inner case is placed in the inner case, one of two metallic spring terminals each having a lead external terminal extended substantially at 45xc2x0 relative to the two legs is arranged on the front surface of the piezoelectric resonator to press the nodes at two opposed positions, and the other metallic spring terminal is arranged on the back surface of the piezoelectric resonator to press the nodes at the remaining two positions.
A lead type piezoelectric component can be constructed by use of the piezoelectric resonator according to the above-described preferred embodiment of the present invention. Thus, the lead-type piezoelectric component has a greatly reduced and very small size while still using the same service frequency band.
Moreover, since the piezoelectric resonator is pressed only at two positions on the front surface and at two positions on the back surface thereof different from those on the front surface, damping of the vibration of the piezoelectric resonator is prevented. Further, though one of the two metallic spring terminals presses the nodes at the two positions and the other presses the nodes at two positions that are different from the above-mentioned positions, the two metallic spring terminals of the same shape and size can be used and their leads can be led out in a substantially parallel manner, since the two metallic spring terminals, each inclined at an angle of about 45xc2x0 relative to the inner case, are placed into the inner case, and the lead type external-terminals each are led out at an angle of about 45xc2x0 relative to the two legs, respectively. Accordingly, the cost of the metallic spring terminals can be greatly reduced.